Volumetric Modulated Arc Therapy (VMAT)

Rotational IMRT delivered during continuous gantry rotation with simultaneously modulated MLC leaves, dose rate, and gantry speed. Delivers conformal dose distributions in 2–6 minutes per fraction — roughly a third to a fifth of conventional step-and-shoot IMRT time. Now the dominant external-beam technique for head / neck, prostate, pelvis, and many other anatomic sites. Branded RapidArc by Varian, VMAT generically by Elekta and TPS vendors.

Clinical pathway

CT simulation with immobilization (mask, Vac-Lok, prone breast board, etc.) and IV contrast as indicated.
Contouring — GTV, CTV, PTV, OARs; often fused with MRI or PET.
Inverse planning — VMAT optimization in Eclipse (Varian), RayStation, Monaco (Elekta), or Pinnacle, with 1–4 arcs, partial or full.
Plan review + QA — patient-specific IMRT QA (portal dosimetry, ArcCheck, Delta4) before first fraction.
Daily treatment — kV-kV or CBCT image guidance, couch shift, delivery.

Typical systems

Varian TrueBeam family
Varian TrueBeam STx
Varian Edge
Varian Halcyon
Elekta Versa HD
Elekta Infinity
Accuray Radixact (helical IMRT, adjacent technique)

Room + procedure characteristics

Delivery time: 2–6 min per fraction.
Dose rate: typically 600 MU/min on flattened beams; FFF plans run 1200–2400 MU/min.
QA: TG-142 daily, monthly, annual; patient-specific IMRT QA before each plan.

Equipment considerations that bite

MLC class is the planning ceiling. Millennium 120 (5 mm) is fine for routine VMAT; HD120 (2.5 mm central) and Agility (5 mm Elekta) handle finer-pitch SRS / SBRT planning. Plan-quality differences are real and physicist-visible.
License tier — RapidArc (Varian) is a separately licensed feature on some chassis configurations. Confirm in writing on refurb.
Imaging chain — kV CBCT quality drives setup accuracy; a tired imager pushes safety margin and dose to OARs.
Dose-rate control electronics — VMAT relies on synchronized leaf-position, dose-rate, and gantry-speed control. Drift in any of the three is a TG-142 fail.
Treatment-planning system compatibility — Eclipse (Varian) ↔ ARIA, Monaco (Elekta) ↔ MOSAIQ, RayStation cross-platform. Switching ecosystems on refurb is a months-long re-commissioning event.

Operational reality

Throughput is the case for VMAT. A site that converts step-and-shoot IMRT to VMAT recovers 5–15 minutes per fraction; over a daily schedule that's 4–8 additional patients with the same machine and staff.
Patient-specific QA is the bottleneck on go-live, not the planning. A new VMAT program staffs up physics labor, not just hardware.
Commissioning for VMAT on a new chassis is weeks of physicist time. Refurb decisions that change MLC class or recon engine carry that cost.